1. Field of the Invention
The present invention relates to a sun and planet gear mechanism.
2. Description Related to the Prior Art
A sun and planet gear mechanisms is widely used as a clutch mechanism which selectively transmits the drive of a motor to a gear train in accordance with a direction of the rotation of the sun and planet gear mechanism caused by the motor. The sun and planet gear mechanism is constructed of a fixed shaft, a sun gear rotatable around the fixed shaft, a planet lever and a planet gear supported by the planet lever. The planet lever swings in the same rotational direction of the sun gear. Accordingly, the planet gear revolves around the fixed shaft to mesh with one of the two gear trains. For changing the gear train with which the planet gear meshes, the swing of the planet gear is necessary. The Japanese Patent Laid-open Publication No. H11-52461 supposes an improvement of the sun and planet gear mechanism for easy swing of the planet lever.
As shown in FIG. 7 and 8, the sun and planet gear mechanism disclosed in the above Publication is constructed a sun gear 2, two planet gears 3, 4, a planet lever 5 and a fixed shaft 6. The planet lever 5 is V-shaped and has two arms. On a crossed position of two arms is formed a shaft cylinder 5a, and in ends of the respective arms are formed gear shafts 5b, 5c. The shaft cylinder 5a fits in a hole 2a formed in the sun gear 2. The gear shafts 5b, 5c is inserted in shaft holes 3a, 4a formed the planet gears 3, 4 so as to rotatably support them. The shaft cylinder 5 has a hole 5d in which the fixed shaft 6 is inserted.
In the sun gear 2, a ring-shape groove 2b is formed around a rotational axis 7. Into the groove 2b are inserted elastic protrusions 5e, 5f formed so as to protrude from the planet lever 5 upwards with inclination. When the sun and planet gear mechanism is assembled, the fixed shaft 6 is inserted in the hole 5d of the planet lever 5, and then the shaft cylinder 5a of the planet lever 5 is inserted into the shaft hole 2a of the sun gear 2. Thereby the two elastic protrusions 5e, 5f enter in the groove 2b of the sun gear 2 and presses an outer wall 2c of the groove 2b. When the sun gear 2 rotates, there is a friction between the outer wall 2c and the elastic protrusions 5e, 5f. According to the friction, the planet gear 5 swings by following the rotation of the sun gear 2. Therefore, the planet gears 3, 4 revolve.
However, as the planet lever 5 contacts the fixed shaft 6, there is a contact resistance between the hole 5d and the fixed shaft 6. Therefore, a force of the rotation of the sun gear 2 is not enough transmitted to the planet lever 5. Therefore the sun gear often does not rotate smoothly. In this case, the planet gears hardly revolve.
An object of the present invention is to provide a sun and planet gear mechanism in which a planet gear revolve smoothly.
Another object of the present invention is to provide a sun and planet gear mechanism in which a contact resistance is small.
In order to achieve the object and the other object, in a sun and planet gear mechanism of the present invention, a sun gear is rotatably fitted on a fixed shaft. A part of the sun gear contacts to a planet lever to generate a frictional force. Accordingly, when the sun gear rotates, the frictional force causes to swing the planet lever. In the sun gear is formed a cylindrical portion in which the fixed shaft is fitted, and in the planet lever is formed a shaft cylinder in which the cylindrical portion is fitted. The shaft cylinder can move on a periphery of the cylindrical portion of the sun gear smoothly.
Further, the planet lever has a contact portion for fitting to a groove which is formed around the cylindrical portion of the sun gear. As there is an adequate friction between the contact portion and the periphery, the rotation of the sun gear is transmitted to the planet lever.
According to the sun and planet gear mechanism of the present invention, the sun gear is fitted on the rotary shaft, a contact resistance may be decreased while the rotation of the sun gear is transmitted to the planet lever. Therefore, the planet lever is smoothly swung.